The present disclosure generally relates to the gain control of a signal in communication systems, and more specifically to the automatic gain control (“AGC”) of a signal detected by a receiver.
To regulate the received signal strength, an adaptive and fundamental mechanism known as AGC is employed. For a weak or attenuated signal, AGC raises the receiver gain stages to bring the signal level to an acceptable signal to noise ratio. Should the received signal strength be strong, then AGC effectively reduces the receiver gain stages to avoid distortion or nonlinear degradations. AGC thus may enable proper reception in the presence of interferers/blockers, as well as bring the required signal to a linear region of reception for certain types of modulations. Stated differently, if done correctly, AGC increases the receiver's dynamic range, which is a critical parameter influencing the receiver's performance.
The details and complexity of the AGC mechanism are dependent on the relevant standard requirements, and the specific selected receiver architecture and its implementation. A wise AGC concept is one that not only complies with the standards, but also contributes to simpler and cost-efficient receiver architecture because time is a critical component to the reception process.
In particular, one of the main bottlenecks in the reception process is the limited amount of time budgeted to prepare the receiver for data reception. For example, in a relatively short period, the receiver has to do some or all of the following tasks: DC Offset compensation, signal presence detection, AGC, frequency offset compensation, symbol synchronization, channel estimation, etc.
In some cases, the timing budgeted for the above tasks, as set forth by the standard, is further shortened due to receiver implementation constraints, such as long PLL settling time, antenna diversity, etc., or specific applications with very strict requirements, such as long sleep intervals without drift correction, large propagation delays, and the like. While the duration for many reception tasks is fairly deterministic and derived from the standard, AGC duration depends on its specific algorithm details and the receiver structure.
In short, AGC duration is a critical element in the sequence of operations that prepare the receiver for proper reception. As illustrated in FIG. 1, present techniques for AGC may involve putting the receiver in certain gain states according to the AGC progression, and doing so without splitting the AGC activity between the I and Q branches. For example, for a certain receiver, AGC may start from the highest gain state that is suitable for achieving sensitivity (longest range). Then according to saturation detection status and/or recognized signal strength indicator (“RSSI”) measurement—based on both I and Q branches—processing the next state of the whole receiver is determined. Such techniques are inadequate.
Accordingly, a device and method of fast automatic gain control in quadrature receivers are therefore desired.